Direct conversion receivers can make receivers smaller, lighter, and lower in power consumption than superheterodyne ones. With these advantages, it is of great merit to use direct conversion receivers as receivers that handle millimeter wave high-frequency signals as in cellular receivers and receivers that are compatible with the IEEE (Institute of Electrical and Electronics Engineers) 802.11a/b/g standards.
In direct conversion receivers, a DC offset that is specific to the receiver circuit configuration occurs when a high-frequency reception signal is down-converted into a baseband one. In contrast, for example, in the direct conversion receiver that is disclosed in Patent document 1, a highpass filter is inserted between a variable gain amplifier and an A/D converter and a DC offset is eliminated by a capacitor that is part of the highpass filter. However, the insertion of the highpass filter in the signal path increases the AGC (automatic gain control) convergence time in the receiver.